Many people wear a cap when swimming or bathing. Prior art caps do not provide a comfortable and convenient solution for protecting a user's hair from getting wet when submerged in water, or when engaged in vigorous activity in water, such as swimming. For example, some caps are overly bulky, uncomfortably tight, or require straps under the user's chin, etc. Others are light and comfortable. However, none of these caps adequately prevent a user's hair from getting wet. For example, they do not have an effective mechanism for preventing the volume of hair placed into the cap from affecting the tightness of the margin, which tightness minimizes water entry. In addition, they do not have a mechanism that effectively minimizes the gaps between the cap and the wearer's head caused by the protrusion of the ears and natural curvatures of the neck. In addition, none of these caps have a mechanism for keeping the tension of the cap shell from causing the cap to retract (i.e., ride up) when the wearer is engaged in movement such as swimming.